This invention relates to an exhaust system having a valve for reducing noise, vibration and harshness (NVH). In particular, the invention relates to an electrically controlled in-muffler exhaust valve for displacement on demand internal combustion engines.
Automobile manufacturers are continuing to develop vehicles having greater fuel economy. In particular, larger vehicles having larger displacement engines have been targeted for better fuel economy. One solution to provide a more fuel efficient vehicle is so-called displacement on demand engines that have cylinder selectively activated depending upon operating conditions. For example, a V-8 operates in V-8 mode when the vehicle requires more power such as towing a trailer. The powertrain control system deactivates four of the cylinders so that the engine operates in V-4 mode when the vehicle requires less power such as when it is lightly loaded and cruising at highway speeds.
One challenge of commercializing displacement on demand engine configurations is that the change between engine modes must be transparent to the vehicle operator. Typically the exhaust system, and in particular the muffler, are tuned so that NVH are minimized when in V-8 mode. However, when the cylinders are deactivated to change from V-8 to V-4 mode the exhaust system produces a tinny or hollow sound considered undesirable to the vehicle operator. To reduce NVH issues when changing from V-8 mode to V-4 mode, an exhaust valve has been used upstream of the muffler behind the catalytic converter. The exhaust valve blocks exhaust flow to increase back pressure and reflects sound wave energy to reduce the low frequency noise levels experienced in V-4 mode.
One prior solution utilizes a cast iron housing arranged between the muffler and catalytic converter. A valve arranged in the cast iron housing is actuated by a vacuum actuator. Vacuum hoses must be routed a considerable length from the engine to the exhaust system to operate the vacuum actuator. The cast housing has considerable weight and presents reliability issues and increased assembly attributable to the connections between the cast housing and the adjacent exhaust system components. Furthermore, the vacuum actuator presents reliability issues resulting from the considerable length the vacuum hoses and connections, which may be damaged during off road vehicle use or assembly at the vehicle assembly plant. Moreover, since the actuator is vacuum operated, limited control over the valve is possible since its operation is based upon engine manifold pressure. Furthermore, the vacuum actuator lacks safeguards in the event of an actuator or valve malfunction.
Therefore, what is needed is an improved powertrain system providing variable tuning in, for example, displacement on demand engine configurations.